Unfair overdue fees app**** on my account.

My overdue amount for Aug was R499 and I made a payment of R1200.00. Which was more than the total amount due for the month but then Woolworths app**** the fee on the entire payment I made instead of the overdue balance. The samething happened in June. I feel Woolworths is unfairly enriching itself by penalizing me for trying to do right. I'm taking 2 steps forward they taking 5 steps. backwards. I've asked for a direct link governing these fees and I still haven't gotten it.